The ets proteins bind DNA, in a sequence-specific manner, to purine-rich sequences found in the promoter/enhancer elements of a variety of genes. The members of the ets family of proteins are transcriptional activators, and induce transcription via binding to a purine-rich consensus sequence (AGGAA). We studied the function and regulation of the ets family of genes, and have shown that ets-I is autoregulated and the overexpression of ets-I and ets-2 proto-oncogenes transforms mouse fibroblasts. The ets-I promoter contains sequences identical to the PEA3 motif; therefore, to examine whether the ets-I protein is able to bind to the PEA3 motif localized in the ets-1 promoter, we synthesized oligonucleotides corresponding to the ets recognition site, as well as unrelated regions from the ets-1 promoter, and tested their binding activity. The v-ets/ets-I protein we synthesized in E. coli binds to sequences derived from the ets-I promoter, as well as MSV LTR and polyoma enhancer (PEA3) derived sequences, but not to unrelated sequences that lack the core elements of the ets recognition site. Thus, it is likely that the ets-1 protein binds to its own promoter in order to autoregulate its expression. In order to investigate whether the ets genes regulate the expression of other gene promoters, we have started testing the activation of MHC class I promoters linked to the CAT reporter gene as a model system after cotransfection with the beta-actin promoter linked ets-1 and ets-2 gene expression vectors. The ets family members (ets-1, ets-2 and erg) have weak homology with the helix-loop-helix protein. To delineate the transactivation domain in ets proteins, and to investigate whether the ets gene is similar to other helix-loop-helix family proteins (El2, E47, myoD), as well as determine if the helix-loop-helix homology region in ets plays a role in the transactivation process, we have linked the ets-I and ets-2 genes in frame with the GAL4 DNA binding domain. Using the ets expression vector, pSG424, we tested for transactivation ability after cotransfection with a reporter plasmid containing the CAT gene linked to the GAL4 promoter and DNA binding site.